The invention relates to control systems which precisely align electrical components, both as to angular orientation and coordinate (X,Y) location for precise placement via pick-and-place systems such as surface mount component placement machines. More specifically, the invention relates to a non-contact laser based sensor system which precisely determines and allows a pick-and-place system to connect the angular orientation of a component and the coordinate positioning of the component for precise placement of the component by a component placement machine on a circuit board or other work surface.
There are two types of component placement machines in common use today, one of which is a cartesian system where one or more vacuum quills are used to travel to a bin, pick up a component, properly orient the component and carry it to a circuit board or other work piece to precisely place the component in its proper location with the leads making proper contact with the circuit connections which are subscribed on the circuit board or work place. Another type of placement system in use is a carousel or turret placement system where components are picked up from the bin and stepped through stations located around the perimeter of a circular component carrying mechanism for placement on the circuit board. It is believed that the present invention will be most useful with cartesian systems which must accurately place components with the highest degree of speed and accuracy.
The electrical components must be placed precisely on the circuit board, to ensure proper electrical contact, thus requiring correct angular orientation and lateral positioning. Angular orientation and lateral positioning are most commonly achieved today through mechanical means. A vacuum quill picks up the part to be placed. During travel between the component bins and the circuit board, four jaws or hammers, which are suspended from the fixturing device, travel downwardly and strike the component on all four sides with substantially equal force. The intent of such a mechanical system is to shift the component on the vacuum quill so it achieves the correct angular orientation, 0 degrees deviation, and also to center it on the vacuum quill. The striking of such components can cause damage such as microcracking of ceramic materials commonly used in capacitors and other such components. It is also extremely difficult to achieve the very high degree of accuracy both as to angular orientation and lateral position that is required by the design rules in use in today's technology where lead spacing and widths are only 10-25 mils wide. To accommodate different component sizes, six different sizes of jaws may be required which can lead to high expense.
A number of non-contact higher precision methods have been proposed. However, light based systems of the past have had difficulty in achieving the high speed and high accuracy which is required for today's technology.
Vision based systems using a TV camera are capable of achieving high accuracy. However, they are one of the most expensive of systems proposed and they require a deviation in the path of the quill from the bin to the TV station, and then to the work piece or circuit board which substantially slows the process. The laser sensor of the instant invention is connected in a manner to surround the component carrying quill which transports the component directly, without deviation, to the appropriate site on the circuit board to achieve a time saving of approximately a factor of two. In addition, it is sometimes difficult to distinguish the particular parameters of very small components being placed by such systems from the quill upon which the components are mounted.
Light sensing systems have also been proposed where a component is interposed in the light path of a collimated beam of light and the intensity of the light is detected by a single photodetector or a pair of photodetectors with a maximum light intensity indicating the narrowest shadow and thus proper angular orientation of the component. However, it is difficult for such systems to handle the range of components that are placed and to achieve the accuracy required for alignment. The dimensions of components to be placed normally vary between 0.02 inch and 2.0 inches. If a single photodetector system is designed large enough to detect shadow variations for a 2.0 inch part, as it must be, the fractional variation caused by rotation of a 0.02 inch part has such little effect on the total light intensity that it is virtually undetectable. For two detector systems, the component part must be precisely aligned between the two detectors with the ratio of light falling on each detector being analyzed to determine edge positions. However, it is extremely difficult to mechanically align photodetectors to make such a measurement. The uniformity of light must be precise and such a system cannot detect component lead positions since shadows of the leads are not distinguishable from shadows of the body of the component.
Finally, it has also been proposed that a series of laser light sources be aligned with a series of laser light detectors. Such a design overcomes some of the problems associated with the proposals for a single detector or pair of detectors. However, the degree of accuracy that can be achieved can be no more than the spacing of the individual laser sources one from the other. The minimum spacing would be given by the size of a laser diode source, which is 0.5 millimeter. This minimum spacing still would be too large for reliable component position detection. The required physical spacing will also be negatively affected by diffraction effects to further limit accuracy of such a design. Also, it is believed that the cost of such a system involving many laser sources would also be prohibitively expensive.
What is needed to achieve component placement for current technology is a component system which can rapidly, in a few hundred milliseconds, align a range of parts varying between 0.02 inches and 2.0 inches with an angular orientation accuracy of less than 0.03.degree. and with lateral position accuracy of better than 0.001 inches. The present invention is specifically addressed to this current need.